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The investment maxim goes "sell in May and go away". And we recently ran a chart that shows that the period from May through to September has been a challenging period for equities.

But Frank Holmes, CEO and Chief Investment Officer of U.S. Global Investors, points to more recent data to note that May has historically been strong for markets.

"Since 1988, the median return for the S&P 500 and MSCI Emerging Markets during May has been 1.22 percent and 1.28 percent, respectively. In fact, May returns rank in the top half for both indices.

This is also a presidential election year in the U.S., which has historically produced positive returns. Since 1972, the stock market has rallied in 5 of the 8 election years, according to J.P. Morgan, with market gains of 12-26 percent. Only during recession years (2000 and 2008) did the S&P 500 provide negative returns."

However, he says June, July, August, and September have been the worst four months of the year for the S&P 500 since 1988. Since 2000 however, the June - September period is split with half the years seeing positive returns, and half seeing negative returns.

Nevertheless, Holmes thinks it's a much better market this year with earnings momentum picking up around the world, and says that instead of selling in May this year, investors should look to global stock markets instead.